Disordered fibrin turnover has been implicated in the pathogenesis of pleural inflammation and repair. We hypothesize that deranged regulation of plasminogen activator inhibitor-1 (PAI-1) and of the urokinase receptor (uPAR) in pleural mesothelial cells are critical determinants of locally impaired fibrinolysis and intrapleural remodeling after asbestos exposure or in fibrosing pleuritis. Mechanisms that regulate expression of these proteins in mesothelial cells are now poorly understood. We will extend work done in previous funding cycles to address these important gaps. We will achieve this objective in four closely integrated specific aims. In Aim 1, we will determine mechanisms that regulate the expression of PAI-1 and uPAR in mesothelial cells exposed to asbestos or mediators of fibrosing pleural injury. In Aims 2 and 3, we will elucidate mechanism(s) by which PAI-1 is regulated by pleural mesothelial cells at the posttranscriptional level and will determine how control at this level influences pathophysiologic responses of these cells. In Aim 4, we will further test a novel interventional approach;intrapleural administration of single-chain uPA (scuPA) to prevent pleural loculation. We will use our established rabbit models of tetracycline- or P. multocida induced pleural injury in these studies. To accomplish the work, we will use a wide range of molecular, biochemical and histologic techniques, all of which are well-established in our laboratory. These studies will foster better understanding of the role of the mesothelial cell in the regulation of the PAI-1-uPA-uPAR system and will increase our understanding of how these cells contribute to pleural remodeling after injury. The project will also facilitate the development of novel, clinically applicable non-surgical approaches to prevent intrapleural loculation and its associated morbidity.